Gantry for medical particle therapy facility

ABSTRACT

A particle therapy gantry for delivering a particle beam to a patient includes a beam tube having a curvature defining a particle beam path and a plurality of superconducting, variable field magnets sequentially arranged along the beam tube for guiding the particle beam along the particle path. In a method for delivering a particle beam to a patient through a gantry, a particle beam is guided by a plurality of variable field magnets sequentially arranged along a beam tube of the gantry and the beam is alternately focused and defocused with alternately arranged focusing and defocusing variable field magnets.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S.application Ser. No. 12/511,621, filed Jul. 29, 2009, which is acontinuation-in-part of U.S. application Ser. No. 11/433,644, filed May12, 2006, now U.S. Pat. No. 7,582,886, which is incorporated herein byreference in its entirety for all purposes. This application also claimspriority to U.S. Provisional Application Ser. No. 61/421,780, filed onDec. 10, 2010, which is incorporated herein by reference in its entiretyfor all purposes.

This invention was made with Government support under contract numberDE-AC02-98CH10886, awarded by the U.S. Department of Energy. TheGovernment has certain rights in the invention.

BACKGROUND OF THE INVENTION

The present invention relates generally to a medical cancer therapyfacility and, more particularly, to a medical particle delivery systemhaving a compact gantry design.

It has been known in the art to use a particle accelerator, such as asynchrotron, and a gantry arrangement to deliver a beam of particles,such as protons, from a single source to one of a plurality of patienttreatment stations for cancer therapy. In such systems, the canceroustumor will be hit and destroyed by particles in a precise way with alocalized energy deposition. Thus, the number of ion interactions on theway to the tumor through the healthy body cells is dramatically smallerthan by any other radiation method. A position of the center of thetumor inside the body defines a value of the particle energy. Thetransverse beam raster is defined by the transverse size of the tumorwith respect to the beam, while the width of the tumor defines the beamenergy range. The energy deposition is localized around the “Bragg” peakof the “implanted particles” and remaining energy is lost due toparticle interaction with the tumor cells.

Such cancer treatment facilities are widely known throughout the world.For example, U.S. Pat. No. 4,870,287 to Cole et al. discloses amulti-station proton beam therapy system for selectively generating andtransporting proton beams from a single proton source and accelerator toone of a plurality of patient treatment stations each having a rotatablegantry for delivering the proton beams at different angles to thepatients. A duoplasmatron ion source generates the protons which arethen injected into an accelerator at 1.7 MeV. The accelerator is asynchrotron containing ring dipoles, zero-gradient dipoles with edgefocusing, vertical trim dipoles, horizontal trim dipoles, trimquadrupoles and extraction Lambertson magnets.

The beam delivery portion of the Cole et al. system includes aswitchyard and gantry arrangement. The switchyard utilizes switchingmagnets that selectively direct the proton beam to the desired patienttreatment station. Each patient treatment station includes a gantryhaving an arrangement of bending dipole magnets and focusing quadrupolemagnets. The gantry is fully rotatable about a given axis so that theproton beam may be delivered at any desired angle to the patient.

The gantry of typical particle beam cancer therapy systems accepts aparticle beam of a required energy from the accelerator and projects itwith a high precision toward a cancerous tumor within a patient. Thebeam from the isocentric gantry must be angularly adjustable so that thebeam can be directed into the patient from above and all sides. Becauseof these requirements, the gantry of a conventional particle beam cancertherapy facility is typically the most expensive piece of equipment ofthe treatment facility and its magnets are generally very large andheavy.

For example, the proton-carbon medical therapy facility described by R.Fuchs and P. Emde in “The Heavy Ion Gantry of the HICAT Facility”includes an isocentric gantry system for delivery of protons, Helium,Carbon and Oxygen ions to patients. The gantry system has a total weightof 630 tons and the required beam line elements for transporting anddelivering fully stripped Carbon and Oxygen ions with 430 MeV/nucleonkinetic energy have a total weight of 135 tons. The rotating part of theisocentric gantry system weighs about 570 tons due to its role to safelytransport and precisely delivers ions to the patients.

Advances in particle accelerator design have resulted in acceleratorsutilizing smaller and less complex magnet arrangements. For example, anonscaling fixed field alternating gradient (FFAG) accelerator hasrecently been developed which utilizes fixed field magnets, as opposedto much larger and more complex variable magnetic field coil magnets.Such advances, however, have heretofore not been applied to the gantrydesign of typical cancer therapy facilities.

Accordingly, it would be desirable to improve upon the prior, artmedical cancer therapy facilities by providing a simpler, less expensiveand more compact gantry design utilizing some of the advances made inthe field of particle accelerators.

SUMMARY OF THE INVENTION

The present invention is a particle therapy gantry for delivering aparticle beam to a patient. The gantry generally includes a beam tubedimensioned for use in a patient treatment room to direct a particlebeam provided thereto to a patient and having a curvature defining aparticle beam path and a plurality of magnets sequentially arrangedalong the beam tube for guiding the particle beam along the particlepath.

In a preferred embodiment, each of the magnets of the gantry is acombined function magnet performing a first function of bending theparticle beam along the particle path and a second function of focusingor defocusing the particle beam. Also, the magnets are preferablyarranged in triplets, wherein each triplet has two focusing magnets andone defocusing magnet disposed between the focusing magnets. Thefocusing magnets perform the combined function of bending the particlebeam and focusing the particle beam and the defocusing magnet performsthe combined function of bending the particle beam and defocusing theparticle beam.

In one embodiment, the magnets are fixed-field, permanent magnetsincluding a ferromagnetic core having a curvature defined by a center ofcurvature and forming a beam tube receiving cavity having the beam tubesupported therein. The core is shaped to provide a magnetic field in thebeam tube which grows stronger in a direction toward the core center ofcurvature. In this embodiment, the defocusing magnets are preferablypositive bending magnets for bending the particle beam along an arcdefined by a positive center of curvature and the focusing magnets arepreferably negative bending magnets for bending the particle beam alongan arc defined by a negative center of curvature, wherein the positiveand negative centers of curvature are oriented on opposite sides of thebeam pipe.

In an alternative embodiment, the magnets are fixed-fieldsuperconducting magnets, which include superconducting coils adjacentthe beam tube for providing the combined function. In anotheralternative embodiment, the magnets are variable-field superconductingmagnets, which include current adjustable superconducting coils adjacentthe beam tube for providing the combined function.

In each case, the beam tube of the gantry preferably includes a particlebeam entry point, a transition point, a particle beam exit point, afirst curved particle beam path arc length extending between the entrypoint and the transition point and a second curved particle beam patharc length extending between the transition point and the exit point.The first arc length bends about ninety degrees and the second arclength bends about one hundred eighty degrees in a direction oppositethe first arc length. Two half-triplets are preferably disposed injuxtaposed orientation at the beam tube transition point and ahalf-triplet is preferably disposed at each of the beam tube entry pointand the beam tube exit point. Each of the half-triplets includes adefocusing magnet and a focusing magnet.

The present invention further involves a method for delivering aparticle beam to a patient through a gantry. The method generallyincludes the steps of bending the particle beam with a plurality ofmagnets sequentially arranged along a beam tube of the gantry, whereinthe particle beam travels in the beam tube, and alternately focusing anddefocusing the particle beam traveling in the beam tube with alternatelyarranged combined function focusing and defocusing magnets.

In a preferred embodiment, the combined function magnets are fixed fieldmagnets arranged in triplets, wherein each triplet includes two focusingmagnets and one defocusing magnet disposed between the focusing magnets.The focusing magnets perform the combined function of bending theparticle beam and focusing the particle beam and the defocusing magnetperforms the combined function of bending the particle beam anddefocusing the particle beam. The defocusing magnets are preferablypositive bending magnets for bending the particle beam along an arcdefined by a positive center of curvature and the focusing magnets arepreferably negative bending magnets for bending the particle beam alongan arc defined by a negative center of curvature, wherein the positiveand negative centers of curvature are oriented on opposite sides of thebeam pipe.

In the embodiment where variable-field magnets are used, these magnetsare combined function superconducting magnets that are also arranged intriplets, wherein each triplet includes two focusing magnets and adefocusing magnet disposed between the focusing magnets. Again, thefocusing magnets perform the combined function of bending the particlebeam and focusing the particle beam and the defocusing magnet performsthe combined function of bending the particle beam and defocusing theparticle beam. In this case, however, both the focusing and defocusingmagnets are positive bending magnets for bending the particle beam alongan arc defined by a positive center of curvature, wherein the positivecenter of curvature is oriented on the inside of the arc of the beampipe.

In this embodiment, the variable field magnets preferably include asuperconducting coil winding surrounding the beam tube and a housingsurrounding the coil winding. The coil winding has a geometry adapted toprovide the combined function and the housing has a curvature defined bya center of curvature and forms a beam tube receiving cavity having thebeam tube supported therein.

Also in this embodiment, the gantry preferably includes two scanningmagnets disposed at a point about 2-3 meters above the patient, whichtranslates to a point about one hundred twenty degrees from thetransition point along the second curved particle beam path arc length.The first dipole scanning magnet provides the required strengths to bendthe beam in either horizontal or vertical transverse planes, while thesecond dipole magnet is provided for adjusting the beam direction to benormal to the patient skin. This is to reduce the amount of skinradiation to the smallest possible value.

Preferably following the two scanning magnets is a superconductingvariable field magnet triplet. The superconducting variable field magnettriplet includes two focusing magnets and a defocusing magnet disposedafter the isocentric gantry. The triplet magnets' role is to define thebeam spot size at the patient. The three magnets provide beam focusingand bending, as they are also combined function magnets.

In a method utilizing variable field magnets according to the presentinvention, a particle beam is delivered to a patient through a gantry bybending the particle beam with a plurality of variable field magnetssequentially arranged along a beam tube of the gantry, adjusting themagnetic field of the variable field magnets based on the energy of theparticles in the particle beam, alternately focusing and defocusing theparticle beam traveling in the beam tube with alternately arrangedcombined function focusing and defocusing variable field magnets anddelivering the particle beam from the gantry to a patient, wherein thebeam is strongly focused in both the horizontal and vertical planes witha very small dispersion function. The step of adjusting the magneticfield of the variable field magnets preferably includes the step ofvarying electrical current to the superconducting coil windings of thevariable field magnets with a controller and the step of alternatelyfocusing and defocusing the particle beam preferably includes the stepof alternating the polarity of the electrical current to thesuperconducting coil winding.

It is also within the scope of the present invention to replace thecombined function magnets with separate function fixed-field permanentmagnets for proton cancer therapy. In this embodiment, the fixed-fieldpermanent magnets are arranged in a series of unit cells, wherein eachcell includes two bending dipole magnets, a focusing quadrupole magnetand two defocusing quadrupole magnets. The bending dipole magnetsperform the function of bending the particle beam along the particlebeam path, the focusing quadrupole magnet performs the function offocusing the particle beam along the particle beam path and thedefocusing quadrupole magnets perform the function of defocusing theparticle beam along the particle beam path.

The bending dipole magnets are preferably separated by the defocusingquadrupole magnet and flanked by the focusing quadrupole magnet. In thismanner, the unit cell is symmetric with respect to the longitudinalcenter of the defocusing quadrupole magnet.

The defocusing quadrupole magnet has a linear horizontal defocusinggradient, whereby particles of the beam path tend to disperse along aplane defined by a radius of curvature of the beam tube, but tend toconcentrate with respect to a plane perpendicular to the radius ofcurvature. Conversely, the two focusing quadrupole magnets have a linearhorizontal focusing gradient, whereby particles tend to concentratealong the plane defined by the radius of curvature of the beam tube, buttend to disperse along the plane perpendicular to the plane defined bythe radius of curvature of the beam tube.

Each of the fixed field permanent magnets preferably include a pluralityof ferromagnetic segments radially arranged around a magnet center,wherein each segment has a fixed magnetic field oriented in apredetermined direction. The bending dipole magnet can include eight orsixteen of these segments arranged to produce a combined dipole magneticfield across the magnet center. Each of the quadrupole magnets can alsoinclude sixteen of these segments arranged to produce a quadrupolemagnetic field across the magnet center.

The beam tube has a radial center line, and each of the defocusingquadrupole magnets is rotated about the beam tube center line to producea quadrupole magnetic field that flows from a plane perpendicular to aplane defined by a radius of curvature of the beam tube to the planedefined by the radius of curvature of the beam tube. Each of thefocusing quadrupole magnets is rotated about the beam tube center ninetydegrees with respect to the defocusing quadrupole magnets to produce aquadrupole magnetic field that flows from the plane defined by theradius of curvature of the beam tube to the plane perpendicular to theplane defined by the radius of curvature of the beam tube.

The gantry may include a particle beam entry point, a transition point,a particle beam exit point, a first curved particle beam path arc lengthextending between the entry point and the transition point and a secondcurved particle beam path arc length extending between the transitionpoint and the exit point. The first arc length bends about ninetydegrees and the second arc length bends about one hundred eighty degreesin a direction opposite the first arc length. In this case, the fixedfield magnets include two half-cells disposed in juxtaposed orientationat the beam tube transition point, a half-cell disposed at the beam tubeentry point and a half-cell disposed at the beam tube exit point. Eachof the half-cells includes a bending dipole magnet, a defocusingquadrupole magnet and a focusing quadrupole magnet.

According to a method of this alternative embodiment of the presentinvention, the particle beam is bent with a plurality of fixed fieldpermanent magnets sequentially arranged along a beam tube of the gantry,the particle beam is alternately focused and defocused with alternatelyarranged focusing and defocusing fixed field permanent magnets and theparticle beam is delivered from the gantry to a patient, wherein thebeam is strongly focused in both the horizontal and vertical planes.

In each of the above described embodiments, the gantry of the presentinvention may be utilized in a medical particle beam therapy systemhaving a source of particles, a particle accelerator, an injector fortransporting particles from the source to the accelerator, one or morepatient treatment stations including rotatable gantries of the presentinvention for delivering a particle beam to a patient and a beamtransport system for transporting the accelerated beam from theaccelerator to the patient treatment station.

The preferred embodiments of the particle beam gantry of the presentinvention, as well as other objects, features and advantages of thisinvention will be apparent from the following detailed description,which is to be read in conjunction with the accompanying drawings. Thescope of the invention will be pointed out in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a typical medical particle delivery therapyfacility.

FIG. 2 is a side view of the arrangement of the gantry treatment room ofthe medical facility shown in FIG. 1.

FIG. 3 is a cross-sectional view of the gantry according to the presentinvention.

FIG. 4 is a graphical representation of one of the magnet tripletsforming the gantry of the present invention.

FIG. 5 is another a graphical representation of one of the magnettriplets forming the gantry of the present invention.

FIG. 6 is an isometric view of one of the magnet triplets forming thegantry of the present invention.

FIG. 7 is a graph showing the horizontal and vertical betatron functionsand the dispersion function of a magnet triplet at the referencemomentum.

FIG. 8 is a graph showing the minimum required aperture for a combinedfunction magnet with a defocusing gradient.

FIG. 9 is a graph showing the minimum required aperture for a combinedfunction magnet with an opposite bend and focusing field.

FIG. 10 is a cross-sectional view of the combined functionbending/defocusing magnet shown in FIG. 5, taken along line 10-10.

FIG. 11 is a cross-sectional view of the combined functionbending/focusing magnet shown in FIG. 5, taken along line 11-11.

FIG. 12 is a cross-sectional view of a fixed field combined functionmagnet utilizing superconducting tapes or coils without an iron core.

FIG. 13 shows a cross-sectional view of a similar fixed fieldsuperconducting magnet having a super ferric core and superconductingcoils surrounding the beam tube.

FIG. 14 is a cross-sectional view of an alternative embodiment of thegantry according to the present invention, wherein variable-fieldcombined function magnets are used.

FIG. 14 a is an enlarged diagrammatic representation of a modifiedmagnet triplet provided at the beam tube transition point shown in FIG.14.

FIG. 15 is an enlarged diagrammatic representation of one of thevariable field combined function magnet triplets forming the gantryshown in FIG. 14.

FIG. 15 a is a cross-sectional view of one of the magnet housings shownin FIG. 15, taken along the line 15 a-15 a of FIG. 15.

FIG. 16 is a graph depicting the desired magnetic field for asuperconducting, variable field combined function magnet for use in thegantry shown in FIG. 14.

FIG. 17 is a graphical cross-sectional view of the coil windings of anexemplary embodiment of a superconducting, variable field combinedfunction magnet for use in the gantry shown in FIG. 14.

FIG. 18 is a graphical representation of a magnet set forming anotheralternative embodiment of the gantry of the present invention.

FIG. 19 is a cross-sectional view of the dipole bending magnet shown inFIG. 18, taken along line 19-19.

FIG. 20 is a cross-sectional view of the quadrupole defocusing magnetshown in FIG. 18, taken along line 20-20.

FIG. 21 shows one of the magnet segments of the quadrupole magnet shownin FIG. 20.

FIG. 22 is a cross-sectional view of the quadrupole focusing magnetshown in FIG. 18, taken along line 22-22.

FIG. 23 is a cross-sectional view of the alternative embodiment of thegantry according to the present invention.

FIG. 24 is a graph showing the particle tracking of protons withdifferent energies through the gantry according to the alternativeembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a typical medical particle delivery therapy facility 10.The facility 10 generally includes an injector 12, a particleaccelerator 14, and a beam delivery network 16 including a rotatablegantry treatment room 18 for delivering a beam to a patient. The beamdelivery network 16 may also be designed to divert independent beams tovarious other applications as desired. For example, the beam deliverynetwork 16 may be designed to deliver a beam to a beam research room 20and a fixed beam treatment room 22. The research room 20 may be providedfor research and calibration purposes, with an entrance separate fromthe patient areas, while the fixed beam treatment room 22 may includeseparate beam lines for such therapeutic applications, such as eyetreatments.

The beam injector module 12 can be a conventional LINAC or a tandem Vande Graaf injector with an injection kicker, which completes the task ofparticle injection into the accelerator 14. In the case of protonparticles, the injector typically provides proton beam pulses at 30 Hzwith a pulse width varying between 25 and 100 nanoseconds at a deliveredenergy of 7 MeV.

The particle accelerator 14 can be a synchrotron, cyclotron or someother conventional design known in the prior art. The accelerator 14accelerates particles to a desired energy level for extraction anddelivery to the patient treatment rooms 18 and 22. Variation of theextraction energy is achieved by adjusting, for example, an RF frequencywithin the accelerator 14. Again for proton particles, extractiontypically occurs when the kinetic energy of the particles is in therange 60 to 250 MeV.

The beam delivery network 16 connects the accelerator 14 to thetreatment rooms 18 and 22 and the beam research room 20. The network 16generally includes an extraction line 26, a switchyard 28 and aplurality of beam transport lines 30. The switchyard 28 is typically anarrangement of switching magnets for diverting the particle beam to adesired beam line 30. The beam transport lines 30 take the particle beamfrom the switchyard 28 to the different treatment rooms of the facility.

Referring additionally to FIG. 2, the rotatable gantry treatment room 18includes a rotating gantry 24, which is rotatable by plus or minus 200degrees from the vertical about a point of rotation 32 to deliver aparticle beam to a patient 33 at a gantry iso-center 34. The gantrysystem accepts particles already accelerated to a required energy. Thefirst part 24 a of the gantry bends particles within a quarter of acircle for 90 degrees. The second part 24 b of the gantry bends theparticles in a half of a circle and brings the particles straighttowards the required direction 34.

The gantry 24 is constructed as a three-dimensional structure supportedon the treatment room side by a bearing 36 and, on the beam inlet side,by a bearing 38. The gantry 24 is further preferably balanced around itsrotation axis. Gantry movement can be realized by a gear motor/gear ringdrive 40 that allows high precision positioning. Each gantry 24 ispreferably controlled by means of an individual independent computerunit that ensures mutual braking of the main drive units, soft start andsoft deceleration functions, control of the auxiliary drive units forthe treatment room, and supervision of the limit switches. The gantry 24further includes a nozzle 42 for delivering the particle beam to thepatient 33.

Referring now to FIG. 3, the optical components of the gantry 24according to a preferred embodiment of the present invention are shown.The gantry 24 generally includes a hook-shaped beam pipe 44 and a seriesof identical magnet triplets 46 arranged in sequence around the beampipe. The beam pipe 44 can be provided as a continuous pipe, or it canbe assembled from a plurality of beam pipe segments welded or otherwisefastened together in a conventional manner. The beam pipe 44 and themagnet triplets 46 are enclosed in a gantry housing 47.

Referring additionally to FIGS. 4-6, the magnet triplet 46 is consideredthe “unit cell” and contains a relatively long combined functionbending/defocusing magnet (QD) 48 flanked by a pair of shorter combinedfunction bending/focusing magnets (QF) 50. The cell 46 is symmetric withrespect to the center of the defocusing magnet 48.

Thus, the gantry 24 is made of densely packed identical “triplet” cells46. Three combined function magnets make a cell. The central magnet 48produces major bending and has a linear horizontal defocusing gradient.Two smaller identical but opposite bending magnets 50 are placed on bothsides of the major bending magnet 48. They have a linear focusinggradient. Each of the combined function magnets 48 and 50 performs twofunctions. The first function is to bend the particle beam along anorbital path, while the second function is to focus or defocus theparticle beam as it travels around the path. The defocusing magnet (QD)48 has a strong central field and a negative gradient (horizontallydefocusing) at the center, while the focusing magnets (QF) 50 have apositive gradient (horizontally focusing).

Preferably, both magnets 48 and 50 are fixed field dipole-type magnetsusing a very strong focusing and small dispersion function. Thehorizontal and vertical betatron functions βx and βy and the dispersionfunction in the basic cell 46, at the reference momentum, are shown inFIG. 7. The minimum required aperture for the two combined functionfixed-field magnets major bend with the defocusing gradient and theopposite bend with the focusing field are presented in FIGS. 8 and 9,respectively. However, as will be discussed in further detail below, theminimum required beam tube aperture can be dramatically reduced bysubstituting superconducting, variable-field magnets for the fixed fieldmagnets.

In the present fixed-field magnet embodiment, the QD and QF magnets 48and 50 are arranged in a non-scaling, fixed field alternating gradient(FFAG) configuration. Such FFAG configurations have been used before inparticle accelerators, but have heretofore never been proposed in atherapeutic particle delivery gantry of a medical facility.

Also, both types of fixed-field magnets 48 and 50 are somewhatarc-shaped or wedge-shaped when viewed in a direction perpendicular tothe path of the beam pipe 44. Thus, each magnet 48 and 50 is defined byan axis 48 a and 50 a, which may represent the center of curvature inthe case of an arc-shaped magnet, or an intersection point of the twooutside faces in the case of a wedge-shaped magnet.

Each defocusing magnet (QD) 48 of each magnet triplet 46 is arrangedalong the beam pipe 44 so that its axis 48 a falls on the same side ofthe beam pipe 44 as the beam pipe's center of curvature 44 a.Conversely, each flanking pair of focusing (QF) magnets 50 of eachmagnet triplet is arranged along the beam pipe 44 so that their axes 50a falls on the opposite side of the beam pipe 44 as the beam pipe'scenter of curvature 44 a. In this manner, each defocusing magnet (QD) 48can be termed a “positive bending” magnet, wherein the shape andarrangement of this magnet bends the particles passing therethrough in apath generally matching the curvature of the beam pipe, as shown inFIGS. 3-6. Each focusing magnet (QD) 50, on the other hand, can betermed a “negative bending” magnet, wherein the shape and arrangement ofthese magnets bend the particles passing therethrough in a pathgenerally opposite to the curvature of the beam pipe. It has been foundthat such alternating arrangement of positive and negative bendingmagnets results in a particle beam having a reduced dispersion.

Referring now to FIG. 10, each fixed-field defocusing magnet (QD) 48includes a ferromagnetic core 52 made up of an upper 53 and a lower half54 forming a dipole magnet. The upper 53 and lower halves 54 areidentical in cross-section and can be solid ferromagnetic masses, asshown in FIG. 10, or they can be made from a series of stackedlaminates. In either case, the upper core half 53 includes an angledface 53 a and the lower core half includes an angled face 54 a. Theangled faces 53 a and 54 a of the upper and lower core halves 53 and 54face each other and form a beam pipe receiving cavity 56 when the corehalves are assembled together to form the magnet core 52.

Referring to FIG. 11, each fixed-field focusing magnet (QF) 50 issimilarly constructed. Specifically, each focusing magnet 50 includes aferromagnetic core 58 made up of an upper 59 and a lower half 60 forminga dipole magnet. Again, the upper 59 and lower halves 60 can be solidferromagnetic masses or they can be made from a series of stackedlaminates 55. Also, the upper core half 59 includes an angled face 59 aand the lower core half includes an angled face 60 a. The angled faces59 a and 60 a of the upper and lower core halves 59 and 60 face eachother and form a beam pipe receiving cavity 62 when the core halves areassembled together to form the magnet core 58.

As mentioned above, each magnet 48 and 50 is a combined functionfixed-field arc magnet combining the functions of bending the particlebeam and focusing or defocusing the particle beam. The bending functionis achieved by the curvature of the magnet, while the focusing ordefocusing function is achieved by the arrangement of the magnet cores52, 58.

In particular, the upper 53 and the lower 54 halves of the defocusingmagnet core 52 are arranged together respectively above and below thebeam pipe 44 so as to provide a magnetic field in the beam pipe whichgrows stronger in a direction toward the center of curvature 48 a of thecore, as shown in FIG. 10, whereas the upper and the lower halves 59 and60 of a focusing magnet core 58 are arranged together respectively aboveand below the beam pipe so as to provide a magnetic field in the beampipe which grows weaker in a direction toward the center of curvature ofthe defocusing core 48 a, but which grows stronger in a direction towardthe center of curvature 50 a of its own core.

Thus, in a defocusing combined function magnet 48, as shown in FIG. 10,a proton, or other particle, in the beam pipe 44 radially further fromthe core center of curvature 48 a and the beam pipe center of curvature44 a (to the right in FIG. 10) is subject to a weaker magnetic field andbends less, while a proton, or other particle, closer to the beam pipecenter of curvature (to the left in FIG. 10) sees a stronger magneticfield and bends more. This results in a more dispersed horizontalconcentration of protons, but a denser vertical concentration, in thebeam pipe just downstream of a defocusing combined function magnet.

Conversely, in a focusing combined function magnet 50, as shown in FIG.11, a proton, or other particle, in the beam pipe 44 radially furtherfrom the beam pipe center of curvature 44 a, or closer to the corecenter of curvature 50 a, (to the right in FIG. 11) is subject to astronger magnetic field and bends more, while a proton closer to thebeam pipe center of curvature, or away from the core center ofcurvature, (to the left in FIG. 11) sees a weaker magnetic field andbends less. This results in a greater horizontal concentration ofparticles, but a weaker vertical concentration of particles in the beampipe just downstream of a focusing combined function magnet.

The above defocusing effect is achieved by orienting the angled surfaces53 a and 54 a of the upper and lower core halves 53 and 54 of thedefocusing magnet core 52 so that they form an intersection point 64that falls on the same side of the beam pipe 44 as the beam pipe centerof curvature 44 a, as shown in FIG. 10. A focusing magnet 50 is formedby orienting the angled surfaces 59 a and 60 a of the upper and lowercore halves 59 and 60 of the focusing magnet core 58 so that they forman intersection point 66 that falls on the side of the beam pipe 44opposite the beam pipe center of curvature 44 a, as shown in FIG. 11. Inother words, the angled faces 53 a and 54 a of a defocusing magnet 48meet adjacent the inner arc of the beam pipe 44, whereas the angledfaces 59 a and 60 a of a focusing magnet 50 meet adjacent the outer arcof the beam pipe, with respect to the center of curvature 44 a of thebeam pipe.

Accordingly, not only are the positive and negative bending functionsalternately arranged, but also the focusing and defocusing functions ofthe magnets are alternately arranged. Such alternate arrangement of thepositive and negative bending and the focusing and defocusing functionsprovides to the present invention the feature of net strong particlebeam focusing in both horizontal and vertical planes.

Returning to FIG. 3, at the transition point 68 of the gantry 24, wherethe beam pipe 44 reverses its curvature, and/or at the beam entry point70 and/or at the beam exit point 72, modifications of the magnet triplet46 can be utilized to provide the desired bending andfocusing/defocusing functions. For example, a half-triplet 76 consistingof a single negative-bend focusing magnet 50 and a reduced length,positive bend defocusing magnet 48 a can be utilized at the beam entrypoint 70 and/or the beam exit point 72 of the gantry to achieve thedesired bend angle and focusing at these points. Similarly, at the beampipe curvature transition point 68, two half-triplets 76, as describedabove, can be assembled together in a juxtaposed orientation to form a“straight” magnet triplet 78.

As a result of the present invention, the size of the gantry in aparticle therapy facility can be dramatically reduced and the controlsystem for a gantry treatment room can be greatly simplified.Specifically, the gantry 24 can be made about 20 meters long, from therotation point 32 to the iso-center 34, with a height of about 3.2meters. The gantry 24 preferably has a free space of about 1.6 metersfrom the last magnet to the isocenter 34.

Thus, the present gantry invention reduces the weight of the gantrysystem by using a non-scaling Fixed Field Alternating Gradient (FFAG)triplet structure with permanent, superconducting or high-temperaturesuperconducting combined function magnets. This invention allows a veryclose control of focused ion transport through the beam line withdifferent energies but under the fixed magnetic field. The ions aredelivered to the isocentric non-scaling FFAG gantry system at the sameentrance position. This invention can achieve presented goals due to avery large momentum acceptance and very strong focusing properties ofthe non-scaling FFAG structures. The ions with different energiestransported through the system arrive at the end of it with smalldifferences in positions (−2.5 up to +3.2 mm) easily adjusted by theraster-scanning focusing part of the gantry.

For proton therapy systems, the combined function defocusing magnet 48and the combined function focusing magnet 50 used in the gantry can bevery small fixed-field permanent magnets, as described above. Forexample, a suitable magnetic field of about 1.8 T can be achieved usingdefocusing magnets 48 that measure about 6 cm×8 cm×10 cm. For largerparticles, such as carbon, the fixed-field permanent magnets willnecessarily be larger.

Alternatively, for larger particles such as carbon, the magnets canutilize high-temperature superconductor tapes (HTS) or superconductingNiobium-Tin coils to achieve the required greater magnetic fields ofabout 6 T. For example, FIG. 12 shows a cross-section of a fixed fieldcombined function magnet 80 utilizing high-temperature superconductortapes (HTS) or superconducting Niobium-Tin coils 82 surrounding the beamtube 44, without an iron core. FIG. 13 shows a cross-section of asimilar superconducting magnet 84 having a super ferric core 86 andsuperconducting coils 88 surrounding the beam tube 44. Bothsuperconducting magnets 80, 84, according to the first embodiment of thepresent invention, are configured to be fixed-field magnets. Thus, ineither case, in this first embodiment of the present invention, themagnets are still fixed-field magnets.

In an alternative embodiment of the present invention, variable-fieldsuperconducting magnets can be provided to further reduce the overallsize of the gantry. As discussed above, fixed-field magnets provide thebenefit of a simple gantry design and ease of use in terms of gantrycontrol systems. In particular, a fixed-field magnet gantry can bedesigned with a beam tube aperture adapted to accommodate a specifiedrange of particle energies generally necessary for most typical particletherapies. Thus, with fixed-field magnets, operation of the gantry issimplified in that the magnetic field of the magnets need not beadjusted for different particle energy levels. In this case, the size ofthe fixed-field magnets is chosen to provide a beam tube apertureadapted to accommodate the desired range of particle energies.

However, as discussed above, especially with respect to larger particlessuch as carbon, in this alternative embodiment of the present invention,the fixed-field magnets can be replaced with superconductingvariable-field magnets. While use of the gantry may be made slightlymore complicated in terms of the control systems needed to accuratelyvary the electrical current to the variable-field magnets, the size ofthe magnets, and as a result, the overall size of the gantry can bedramatically reduced by using variable-field magnets.

Turning now to FIG. 14, the optical components of the variable fieldgantry 200 according to this alternative embodiment of the presentinvention are shown. Again, the gantry 200 generally includes ahook-shaped beam pipe 202 and a series of identical magnet triplets 204arranged in sequence around the beam pipe. The beam pipe 202 and themagnet triplets 204 are enclosed in a gantry housing (not shown in FIG.14).

Referring additionally to FIG. 15, the magnet triplet 204 is againconsidered the “unit cell” but in this case, the unit cell has avariable-field combined function bending/defocusing magnet (QD) 206flanked by a pair of variable-field combined function bending/focusingmagnets (QF) 208. The cell 204 is symmetric with respect to the centerof the defocusing magnet 208.

Similar to that described above with respect to the fixed-field magnets,the gantry 200 is again made of densely packed identical “triplet” cells204, wherein three variable-field combined function magnets 206, 208make a cell. The central magnet 206 produces major bending and has alinear horizontal defocusing gradient. Two identical positive bendingmagnets 208 are placed on both sides of the major bending magnet 205.These flanking magnets 208 have a linear focusing gradient. Each of thecombined function magnets 206 and 208 performs two functions. The firstfunction is to bend the particle beam along an orbital path, while thesecond function is to focus or defocus the particle beam as it travelsaround the path. The defocusing magnet 206 has a strong central fieldand a horizontally defocusing gradient at the center, while the focusingmagnets 208 have a horizontally focusing gradient.

However, unlike the fixed-field magnets discussed above, thesuperconducting combined function focusing and defocusing magnets 206,208 bend in the same direction. Specifically, the superconductingcombined function focusing and defocusing magnets 206, 208 are positivebending magnets having a curvature matching the curvature of the gantry.More particularly, the focusing and defocusing magnets 206, 208 have acurvature for bending the particle beam along an arc defined by apositive center of curvature, wherein the positive center of curvatureis oriented on the inside of the arc of the beam pipe.

Thus, both types of variable-field magnets 206, 208 are somewhatarc-shaped or wedge-shaped when viewed in a direction perpendicular tothe path of the beam pipe 202. Each magnet 206, 208 includes a beam tubesegment 202 a, a superconducting coil winding 210 surrounding the beamtube segment and a circular housing 212 surrounding the coil winding.

The geometry of the coil winding 210 provides the combined functions ofbending and focusing or defocusing and the polarity of the electricalcurrent provided to the winding determines whether the magnet is afocusing magnet or a defocusing magnet. Thus, virtually identicalsuperconducting magnets can be arranged along the gantry path, with thepolarities of the electrical current to the magnets alternating so as toresult in a defocusing/focusing/defocusing triplet.

For example, the magnetic field can be produced by double-helix coils210 in which the axial path of the windings is defined by a sinusoidalfunction containing the superposition of the desired multi poles. Theresult is a magnet that can contain, for example, a pure dipole fieldwith superimposed multipole fields, whose magnitude relative to thedipole field can be easily controlled to any level. The combinedfunction winding can also be used to superimpose a dipole and quadrupolewinding where the quadrupole integral of Gdl can be adjusted to anylevel desired over the length of the main dipole magnet. In this way a“free” quadrupole can be obtained within a dipole. It follows that, inthe straight section of a long coil, pure multi pole fields can beproduced by pairs of oppositely tilted coil windings with appropriatesinusoidal modulation of the axial position of the turns.

The characteristics of this type of combined function magnet arediscussed by C. Goodzeit, R. Meinke, M. Ball, Advanced Magnet Lab, Inc.,in MOPAS055 Proceedings of PAC07, Albuquerque, N. Mex., USA, COMBINEDFUNCTION MAGNETS USING DOUBLE-HELIX COILS, (2007), which is incorporatedherein by reference. Indeed, suitable combined function variable fieldmagnets for use in the present invention are marketed by Advanced MagnetLab, Inc., Melbourne Fla. 32901. However, the invention is not limitedto the specific design of these magnets and other combined functionvariable field magnets can be utilized.

The essential concept for the design of any of these combined functionvariable field magnets, including the double helix designs discussedabove, is that the required magnetic field for the combined functionmagnet is obtained without use of iron or any other magnetic material.In other words, a very good quality magnetic field is achieved from thesuperconducting coils wound around the curved pipe in which the beampasses through in vacuum.

The coils 210 generally need to be cooled to very low temperatures ofabout 2-4 K. This can be accomplished by providing a flow of liquidhelium around the beam pipe. A typical construction of a magnet assemblyhaving features for supporting and cooling the coil winding 210 is shownin FIG. 15 a. The layer of liquid helium and the superconducting coilwinding 210 are isolated by two additional concentric pipes. The innerhelium pipe 226 contains sheets of kepton 224 or other similartemperature isolating materials, to allow transition to roomtemperature. This inner pipe is coaxially supported within the outermagnet housing 212 by suitable stand-offs 228. The heat transfer betweenthe beam pipe 202 and the outside room temperature pipe 212 has to bevery small (e.g., <4 W). Therefore, the beam pipe 202 and the inner pipe226 are preferably adapted to withstand a temperature difference between2-4K and 70K, while the outer isolation part with vacuum of few mTorr isadapted for a temperature range of 70 K-300 K.

The magnets used in this alternative embodiment of the present inventionare variable-field magnets, meaning that the magnetic field of themagnets can be varied by varying the amplitude of the electrical currentflowing through the coil winding 210. As discussed above, the gantry oftypical particle beam cancer therapy systems accepts a particle beam ofa pre-determined energy from the accelerator, wherein the energy of theparticle beam is determined based on the desired patient therapy. Unlikethe fixed-field magnet embodiment described above, which can accommodatea specified range of particle beam energies, the variable-field magnetsused in this alternative embodiment allows for the adjustment of themagnetic field in the gantry based on the energy level of the particlesbeing delivered to the gantry. In this regard, the gantry of thisalternative embodiment will require a conventional electrical controllerwith a feedback system to accurately vary the electrical currentprovided to the superconducting coils of the variable-field magnets inorder to adjust the magnetic field in the gantry to accommodate theenergy level of the particles delivered to the gantry from theaccelerator.

FIG. 16 shows the desired magnetic field for a direct wind,variable-field, combined function gantry magnet of the presentinvention. FIG. 17 is a cross-section of one embodiment of a coilwinding design of an exemplary superconducting variable-field magnet foruse in the present invention. However, the present invention is notlimited to these magnet designs, and it is conceivable that othervariable-field superconducting magnet designs can be utilized.

In a preferred embodiment, the length of the defocusing magnet 206 ispreferably about 0.3 m and the length of the focusing magnet 208 ispreferably about 0.32 m. The bending fields of the defocusing magnet 206is preferably about 5.585 T and the bending field of the focusing magnet208 is preferably about 3.665 T. The bending angles are Ang-D=0.264 mradfor the defocusing magnet 206 and Ang-F=0.1848 mrad for the focusingmagnet 208 and the gradients are Gd=−80 T/m and Gf=95 T/m for the gantrydefocusing and focusing magnets, respectively.

Under these design considerations, FIG. 14 also shows 400 MeV/u carbonbeam orbits tracked through the gantry 200. The maximum beam size is ±3mm and momentum offsets are in a range of ±5%. This translates to carbonkinetic energy±1.213 MeV) and an estimated beam tube aperture of 2 cmdiameter.

As mentioned above, each magnet 206, 208 is a combined functionvariable-field arc magnet combining the functions of bending theparticle beam and focusing or defocusing the particle beam. The bendingfunction is achieved by the positive curvature of the magnet, while thefocusing or defocusing function is achieved by the arrangement of thesuperconducting coil windings 210 within the magnet housings 212.

Thus, in a defocusing combined function magnet 206 a carbon atom, orother particle, in the beam pipe 202 radially further from the shieldcenter of curvature and the beam pipe center of curvature is subject toa weaker magnetic field and bends less, while the same particle closerto the beam pipe center of curvature sees a stronger magnetic field andbends more. This results in a more dispersed horizontal concentration ofparticles, but a denser vertical concentration, in the beam pipe justdownstream of a defocusing combined function magnet.

Conversely, in a focusing combined function magnet 208, a carbon atom,or other particle, in the beam pipe 202 radially further from the beampipe center of curvature, or closer to the shield center of curvature,is subject to a stronger magnetic field and bends more, while a particlecloser to the beam pipe center of curvature, or away from the shieldcenter of curvature, sees a weaker magnetic field and bends less. Thisresults in a greater horizontal concentration of particles, but a weakervertical concentration of particles in the beam pipe just downstream ofa focusing combined function magnet.

Returning to FIG. 14, at the transition point 214 of the gantry 200,where the beam pipe 202 reverses its curvature, and/or at the beam entrypoint and/or at the beam exit point, modifications of the magnet triplet204 can be utilized, as discussed above with respect to the fixed-fieldmagnets, to provide the desired bending and focusing/defocusingfunctions. For example, a half-triplet consisting of a single focusingmagnet and a reduced length defocusing magnet can be utilized at thebeam entry point and/or the beam exit point of the gantry to achieve thedesired bend angle and focusing at these points.

Similarly, at the beam pipe curvature transition point 214, twohalf-triplets 215, as described above, can be assembled together in ajuxtaposed orientation to form a modified magnet triplet 216, as shownin FIG. 14 a. The modified magnet triplet 216 includes a modifiedcombined function defocusing magnet 206 a at its center. The modifiedcombined function defocusing magnet 206 a is essentially a regulardefocusing magnet 206 which has been cut in half along its length andreassembled so that its two halves now form an S-shape such that thebeam tube undergoes a change in curvature in the opposite direction. Themodified combined function defocusing magnet 206 a is provided at oneend with a combined function focusing magnet 208 a, which bends in onedirection, and is provided at its opposite end with a combined functionfocusing magnet 208 b, which bends in the opposite direction. Thismodified triplet 216 thus provides the change in curvature at the beamtube transition point 214.

An advantageous feature of the combined function variable-field magnetgantry over the combined function fixed-field magnet gantry is that thenumber of magnet cells can be reduced to 12, 14 or 16 cells, as comparedto 38 cells for the fixed-field gantry. With fewer cells, the particleorbit offsets (previously 8-12 mm) can be dramatically reduced to 1 mm.This in turn reduces the size of the combined function variable-fieldmagnets' radial aperture.

In addition, because the number of cells is reduced using combinedfunction variable-field magnets, the final scanning and focusing magnetsdefining the end of the gantry can be located further upstream along thegantry path. In particular, as shown in FIG. 14, the scanning magnets218, necessary to allow a fast spot scanning in transverse planes, arelocated after the gantry arc before or upstream of the full 180 degreeposition 220 of the arc. Moving the scanning magnets 218 back to a point221 that is roughly 120 degrees along the arc of the gantry, results inthe overall height size of the gantry being reduced from 6-8 metersheight to about 3.0 meters, while a distance from the last element tothe patient axis is 0.9 meters. The result is a gantry having a morecompact design.

Reducing the size of the maximum height and length of the isocentricgantry will naturally reduce the installation and operation cost to thecancer treatment facility. This is primarily because the size of thegantry room can be drastically reduced. The cost of the supportstructure, with the necessary counter weight on the opposite side to thegantry, will also be reduced if the weight of the gantry is smaller.Presently, the weight of the gantry of known top-notch facilities isabout 630 tons. This size also requires very large amounts of concreteblocks positioned underneath to allow for the required precision of lessthan 1 mm. The estimated weight of the superconducting gantry of thepresent invention is about 1.5 tons. Such a large difference in weightcomes from the low weight of the superconducting magnets and from thesmall size of the gantry itself.

In this embodiment, the final focusing magnets 222 of the gantry 200 canalso be in the form of a combined function variable-field magnettriplet. In other words, the final focusing magnets are in the form of afocusing/defocusing/focusing triplet 222 and are also combined functionmagnets. The triplet starts with a focusing magnet 208, after thescanning magnets 218, which is 0.3 m long and has a focusing gradient ofGf=36 T/m. The central magnet 206 in the triplet 222 is a defocusingmagnet having a length of Ld=0.32 m and a gradient of Gd=−48 T/m. Thebending angles of the focusing magnets 208 are Ang-FTriplet=O.352 mrad,while for the defocusing magnet 206 of Lf=0.3 m the bending angle isAng-DTriplet=0.2464 mrad.

With conventional cancer therapy systems utilizing proton/carbon ions,the ions reach the cancerous tumors in the body very precisely in threedimensions. Longitudinally, almost all energy is deposited by the Braggpeak, for example at a depth of 27 cm, with 2σ=5.55 mm for the protonbeam with kinetic energy of 206 MeV, or at the same depth of 27 cm forthe carbon beam 2σ=1.61 mm with kinetic energy of 400 MeV/u. The minimumpossible transverse beam size of the proton beam at the same depth of 27cm is 2σ=11.35 mm or for the carbon beam is 2σ=2.93 mm.

A beam spot scanning technique is the typical method used in cancertherapy, wherein the beam is moved in the transverse x and y planes at asingle energy with the scanning magnets. It is preferable to have arange of ±10 cm in both transverse planes, and to reach the patient skinwith beams parallel to each other and with an angle of 90 degrees. Forthis reason, almost all conventional isocentric gantry systems contain avery large aperture (±10 cm) dipole magnet at the end of the gantry.This magnet is a warm temperature sector dipole with an average weightof about 60-70 tons.

By utilizing a combined function variable-field magnet triplet 222 afterthe scanning magnets 218, according to the present invention, acompletely new scanning system is provided in which all requirements fortreatment can be fulfilled without use of extremely large dipole magnetsand with a control of the beam size at the patient and allowance ofarrival of the beam at 90 degrees. The non-scaling FFAG gantry bringsthe beam at the end of the transfer focused at the middle of the firsttransverse scanning magnet. The scanning magnet is a standard warmdipole magnet 30 cm length, with a maximum field of 1 T and the maximumbending angle of θ=30 mrad. This maximum bending angle produces 10 cmorbit offset at the patient. The beam arrives at the scanning magnetwith an angle with respect to the direction to the patient. This is dueto reduction of the height of the gantry.

The triplet combined function magnets provide a beam arrival to thepatient under a normal angle. The aperture size of the triplet magnetsis not very large as they are placed after the horizontal/verticalscanning magnet. An additional vertical/horizontal scanning magnet witha large aperture of ±10 cm could be added for the required normal angleincidence to the patient. It could be placed following the tripletmagnets above the patient.

Also, although transporting ions through the whole required energy rangefor the patient's cancer treatment with the fixed magnetic field gantryembodiment is very advantageous, elements at the end of the gantry,(i.e., the scanning magnets and the triplet focusing combined functionmagnets), required adjustments for each energy treatment. Thisnecessarily required the use of larger and more complex scanning andfocusing magnets at the end of the gantry, which, in turn, increased theoverall size of the gantry. Use of variable-field magnets throughout thegantry eliminates this drawback.

While use of combined function magnets, whether fixed-field orvariable-field, provides the benefits and superior performance asdescribed above, in another alternative embodiment of the gantryaccording to the present invention, the combined function magnetsdescribed above can be replaced by fixed-field, separate function,permanent magnets. As will be discussed in further detail below, suchmagnets are simple and inexpensive to manufacture and can be easilyassembled and adapted to existing medical facility gantries.

Turning now to FIGS. 18-23, the optical components of the gantry 100according to the alternative embodiment of the present invention areshown. Again, the gantry 100 generally includes a hook-shaped beam pipe102 and a series of fixed-field magnets arranged in sequence around thebeam pipe. The beam pipe 102 can be provided as a continuous pipe, or itcan be assembled from a plurality of beam pipe segments welded orotherwise fastened together in a conventional manner. The beam pipe 102and the magnets are enclosed in a gantry housing 104.

However, in place of the combined function magnet triplets describedabove, the gantry in this embodiment is made from a series of unit cells106 having separate function fixed-field permanent magnets 108. Inparticular, each unit cell 106 includes two bending dipole magnets (B)110, separated by a defocusing quadrupole magnet (QD) 112 and flanked bytwo focusing quadrupole magnets (QF/2) 114, as shown in FIG. 18.

As compared to the “combined function” magnets described above, the term“separate function” refers to the fact that each individual magnet 108in this alternative embodiment of the invention performs only onefunction. Specifically, each of the two bending dipole magnets (B) 110only bends the particles along an orbital path around the curvature ofthe gantry 100, without focusing or defocusing the particles. Thedefocusing quadrupole magnet (QD) 112 each only defocuses the particleswithin the beam pipe 102 as they travel around the path, while each ofthe two focusing quadrupole magnets (QF/2) 114 only focus the particlesin the beam pipe.

In this regard, the frame of reference for the terms “defocus” and“focus” is the plane defined by the radius of curvature of the beam pipe102, sometimes referred to herein as the “horizontal” plane. Thus, thedefocusing quadrupole magnet (QD) 112 has a linear horizontal defocusinggradient, wherein particles tend to disperse along the plane defined bythe radius of curvature of the beam pipe 102, but tend to concentratewith respect to the plane perpendicular (“vertical”) to the radius ofcurvature, while the two focusing quadrupole magnets (QF/2) 114 have alinear horizontal focusing gradient wherein particles tend toconcentrate along the plane defined by the radius of curvature of thebeam pipe 102, but tend to disperse along the plane perpendicular(“vertical”) to this plane.

The characteristic differences between the combined function tripletsdescribed above and the separate function unit cells in this alternativeembodiment relate to the fact that, rather than using dipole-typemagnets arranged in a specific manner so as to mimic the performance ofboth a dipole magnet and a quadrupole magnet, the unit cells of thisalternative embodiment include true dipole magnets and true quadrupolemagnets to separate the functions of bending and focusing/defocusing. Inother words, at each point along the beam tube path in the combinedfunction magnet triplet described above, the particles are subject toboth bending and focusing/defocusing magnetic forces. In thisalternative separate function magnet embodiment, at different pointsalong the beam tube path, the particles are only subject to a bendingforce or a focusing/defocusing force. Nevertheless, like the combinedfunction magnets described above, the alternate arrangement of thefocusing and defocusing functions provides to this alternativeembodiment the feature of net strong particle beam focusing in bothhorizontal and vertical planes.

Referring to FIG. 18, the cell 106 is symmetric with respect to thecenter of the defocusing quadrupole magnet (QD) 112. The two bendingdipole magnets 110 are preferably about 4.8 cm long and are orientedalong the beam pipe 102 to bend particles along an arc defined by thebeam pipe center of curvature 101. The quadrupole defocusing magnet 112is preferably about 8 cm long and the two quadrupole focusing magnets114 are each about 5.5 cm long. As a result, the length of the unit cell106 is about 29 cm long.

Thus, the gantry 100 is made of densely packed identical cells 106arranged around the curvature of the beam pipe as shown in FIG. 23. Inan exemplary embodiment twenty-seven cells make up the 180 degree exitportion of the gantry and fourteen cells make up the 90 degree entryportion of the gantry. To fit the curvature of the beam pipe 102, themagnets 108 can be somewhat arc-shaped or wedge-shaped when viewed in adirection perpendicular to the path of the beam pipe 102. However, inthis case, there is no negative bending of the particles, as describedabove, but only positive bending by the two bending dipole magnets (B)110.

Referring specifically to FIGS. 19-22, each magnet 108 is a fixed-fieldpermanent magnet made from a plurality of wedge-shaped or arc-shapedsegments 116 arranged around a radial center 118 of the magnet. Whenassembled around the beam pipe 102, the radial center 118 of each magnetis aligned with the center 103 of the beam pipe. The segments 116 aremade from a ferromagnetic material, such as a sintered compound ofNeodymium-Iron-Boron (Nd2Fe14B) or rare earth cobalt (REC), and eachsegment has a fixed magnetic field oriented in a predetermined directionupon manufacture of the segment. For example, certain segments 116 a arefabricated with a fixed magnetic field pointing in a direction from theinner radius 120 of the segment toward the outer radius 122 of thesegment, while other segments 116 b are fabricated with a fixed magneticfield pointing in the opposite direction from the outer radius 122 ofthe segment toward the inner radius 120 of the segment. Other segments116 c are fabricated with a fixed magnetic field pointing in a directionfrom one lateral side 124 of the segment toward the opposite side, whilestill other segments 116 d are fabricated with fixed magnetic fieldspointing in a direction somewhere in between the directions describedabove.

The segments 116 are oriented around the magnet center 118 so as toproduce a dipole magnet 110, as shown in FIG. 19, or a quadrupole magnet112, 114, as shown in FIGS. 20 and 22. More specifically, the segments116 are assembled together so that the individual magnetic fieldorientations of each segment combine together to produce a magnet havinga resultant magnetic field oriented in a desired direction. Thus, adipole bending magnet 110 can be formed by arranging eight segments 116to produce a combined dipole magnetic field 126 across the magnet center118, as shown in FIG. 19, while a quadrupole magnet 112, 114 can beformed by arranging sixteen segments 116 to produce a quadrupolemagnetic field 128 across the magnet center 118, as shown in FIGS. 20and 22. Such fixed-field permanent magnets are known in the art as“Halbach” magnets and are described in Halbach, “Design of PermanentMultipole Magnets With Oriented Rare Earth Cobalt Material,” NuclearInstruments and Methods 169, pp. 1-10 (1980), which is incorporatedherein by reference in its entirety for all purposes.

The focusing or defocusing function of the quadrupole magnets 112, 114is determined by how the respective quadrupole magnet is rotated withrespect to the beam tube center 103. Thus, if a quadrupole magnet isoriented about the beam tube center 103 so that a quadrupole magneticfield flowing from a vertical direction to a horizontal direction isproduced, as shown in FIG. 20, a defocusing magnet 112 is provided alongthe gantry 100. Conversely, if the same quadrupole magnet is rotatedninety degrees with respect to the beam tube center 103, such that themagnetic field now flows from a horizontal direction toward a verticaldirection, as shown in FIG. 22, a focusing magnet 114 is provided alongthe orbital path of the beam pipe 102.

Referring also to FIG. 18, the magnet properties of the preferredembodiment of the unit cell 106 are set forth in the following table.

Br 1.35 T Bg = Br ln (OD/ID) 2.4 T OD 17.75 cm  ID 3.0 cm ln (OD/ID)1.78 QLD 8.0 cm BL 4.8 cm QLF  11 cm GF 2.4 T/0.015 m = 160.0 T/m GD−2.4 T/0.013 m = −180.0 T/m

FIG. 23 also shows proton traces magnified twenty-five times, withenergies in a range of between 68-250 MeV. Tracking results forparticles in this energy range are shown in more detail in FIG. 24.

Thus, with the separate function magnet embodiment for a proton gantryapplication, the maximum achievable magnetic field is between about 2.2to about 2.6 Tesla, and the working energy range for proton energy isbetween about 68 to about 250 MeV. This is due in part to the segmentedstructure of the fixed-field permanent magnets. Specifically, thesegments of the fixed-field magnet are arranged in such a way that eachsegment adds to the magnetic field in a supplemental manner, resultingin a magnet with a magnetic field greater than the magnetic flux of themagnet material of its individual parts. As a result, the magnetsthemselves can be made smaller whereby more magnet cells can be used ina fixed space. More magnet cells increases the focusing strength of thegantry, which in turn reduces the aperture sizing of the gantry nozzle.This allows for a wider momentum energy range of particles for differentmedical applications.

As a result, a simple and easy to assemble magnet unit cell 106 can beprovided for the gantry 100. Specifically, in the combined functionmagnet triplet embodiment described above, wherein the particle bendingfunction is provided by the curvature of the magnet, each magnet must beprecisely positioned to match the curvature of the beam tube. This isfurther complicated when positive and negative bending magnets are used.With this separate function magnet embodiment, wherein the bendingfunction is achieved by the dipole magnetic field produced by the dipolemagnet, matching the curvature of the magnet to the curvature of thebeam tube is less critical.

However, similar to that described above with respect to the combinedfunction magnet triplet cells, modifications of the unit cell may benecessary to fully assemble the gantry. For example, at the transitionpoint 130 of the gantry 100 of this alternative embodiment, where thebeam pipe 102 reverses its curvature, and/or at the beam entry point 132and/or at the beam exit point 134, modifications of the unit cell 106can be utilized to provide the desired bending and focusing/defocusingfunctions. For example, a half cell consisting of a single bendingdipole magnet 110 and a reduced length, defocusing magnet 112 can beutilized at the beam entry point 132 and/or the beam exit point 134 ofthe gantry 100 to achieve the desired bend angle and focusing at thesepoints. Similarly, at the beam pipe curvature transition point 130, twohalf-cells, as described above, can be assembled together in ajuxtaposed orientation to form a “straight” magnet cell.

As a result of the present invention, the size of the gantry in aparticle therapy facility can be dramatically reduced and the controlsystem for a gantry treatment room can be greatly simplified.Specifically, the gantry 24, 100 can be made about 20 meters long, fromthe rotation point 32 to the iso-center 34, with a height of about 3.2meters. Also, the advantages of using permanent magnets include areduction in the number of DC power supplies. Moreover, a very strongfocusing structure is obtained by using small size “Halbach” magnets.

Although preferred embodiments of the present invention have beendescribed herein with reference to the accompanying drawings, it is tobe understood that the invention is not limited to those preciseembodiments and that various other changes and modifications may beaffected herein by one skilled in the art without departing from thescope or spirit of the invention, and that it is intended to claim allsuch changes and modifications that fall within the scope of theinvention.

The invention claimed is:
 1. A particle therapy gantry for delivering aparticle beam to a patient comprising: a beam tube dimensioned for usein a patient treatment room to direct a particle beam provided theretoto a patient and having a curvature defining a particle beam path; and aplurality of variable field magnets sequentially arranged along saidbeam tube for guiding the particle beam along said particle path.
 2. Agantry as defined in claim 1, wherein each of said variable fieldmagnets is a combined function magnet performing a first function ofbending the particle beam along said particle path and a second functionof focusing or defocusing the particle beam.
 3. A gantry as defined inclaim 2, wherein said combined function variable field magnets arearranged in triplets, each triplet comprising two focusing magnets and adefocusing magnet disposed between said focusing magnets, said focusingmagnets performing the combined function of bending the particle beamand focusing the particle beam and said defocusing magnet performing thecombined function of bending the particle beam and defocusing theparticle beam.
 4. A gantry as defined in claim 3, wherein both saidfocusing magnets and said defocusing magnets are positive bendingmagnets for bending the particle beam along an arc defined by a positivecenter of curvature, said positive center of curvature being oriented onthe inside of the arc of said beam pipe.
 5. A gantry as defined in claim4, wherein said variable field magnets comprise: a superconducting coilwinding surrounding said beam tube, said superconducting coil windinghaving a geometry adapted to provide said combined function; and ahousing surrounding said superconducting coil winding, said housinghaving a curvature defined by a center of curvature and forming a beamtube receiving cavity having said beam tube supported therein.
 6. Agantry as defined in claim 3, wherein said beam tube includes a particlebeam entry point, a transition point, a particle beam exit point, afirst curved particle beam path arc length extending between said entrypoint and said transition point and a second curved particle beam patharc length extending between said transition point and said exit point,said first arc length bending about ninety degrees and said second arclength bending about one hundred eighty degrees in a direction oppositesaid first arc length.
 7. A gantry as defined in claim 6, furthercomprising: at least one scanning magnet disposed at a point about onehundred twenty degrees from said transition point along said secondcurved particle beam path arc length; and a superconducting variablefield magnet triplet disposed between said scanning magnet and said beamtube exit point, said superconducting variable field magnet tripletcomprising two focusing magnets and a defocusing magnet disposed betweensaid focusing magnets, said focusing magnets performing the combinedfunction of bending the particle beam and focusing the particle beam andsaid defocusing magnet performing the combined function of bending theparticle beam and defocusing the particle beam.
 8. A gantry as definedin claim 6, wherein said combined function variable field magnetscomprise two half-triplets disposed in juxtaposed orientation at saidbeam tube transition point, each of said half-triplets comprising adefocusing magnet and a focusing magnet, said focusing magnet performingthe combined function of bending the particle beam and focusing theparticle beam and said defocusing magnet performing the combinedfunction of bending the particle beam and defocusing the particle beam.9. A gantry as defined in claim 6, wherein said combined functionvariable field magnets comprise a half-triplet disposed at said beamtube entry point and a half-triplet disposed at said beam tube exitpoint, each of said half-triplets comprising a defocusing magnet and afocusing magnet, said focusing magnet performing the combined functionof bending the particle beam and focusing the particle beam and saiddefocusing magnet performing the combined function of bending theparticle beam and defocusing the particle beam.
 10. A method fordelivering a particle beam to a patient through a gantry comprising thesteps of: bending the particle beam with a plurality of variable fieldmagnets sequentially arranged along a beam tube of the gantry, theparticle beam traveling in said beam tube and said beam tube beingdimensioned for use in a patient treatment room to direct a particlebeam provide thereto to a patient; adjusting the magnetic field of thevariable field magnets based on the energy of the particles in theparticle beam; alternately focusing and defocusing the particle beamtraveling in said beam tube with alternately arranged combined functionfocusing and defocusing variable field magnets; and delivering saidparticle beam from said gantry to a patient, wherein said beam isstrongly focused in both the horizontal and vertical planes.
 11. Amethod as defined in claim 10, wherein said combined function variablefield magnets are arranged in triplets, each triplet comprising twofocusing magnets and a defocusing magnet disposed between said focusingmagnets, said focusing magnets performing the combined function ofbending the particle beam and focusing the particle beam and saiddefocusing magnet performing the combined function of bending theparticle beam and defocusing the particle beam.
 12. A method as definedin claim 11, wherein both said focusing magnets and said defocusingmagnets are positive bending magnets for bending the particle beam alongan arc defined by a positive center of curvature, said positive centerof curvature being oriented on the inside of the arc of said beam pipe.13. A method as defined in claim 11, wherein said variable field magnetscomprise: a superconducting coil winding surrounding said beam tube,said superconducting coil winding having a geometry adapted to providesaid combined function; and a housing surrounding said superconductingcoil winding, said housing having a curvature defined by a center ofcurvature and forming a beam tube receiving cavity having said beam tubesupported therein, and wherein said step of adjusting the magnetic fieldof the variable field magnets comprises the step of varying electricalcurrent to said superconducting coil winding, and wherein said step ofalternately focusing and defocusing the particle beam comprises the stepof alternating the polarity of the electrical current to saidsuperconducting coil winding.
 14. A particle beam therapy systemcomprising: a source of particles; an accelerator for accelerating theparticles to a desired energy level; an injector for transporting theparticles from said source to said accelerator; a patient treatment roomincluding a rotatable gantry for delivering a beam of the acceleratedparticles to a patient, said gantry including a beam tube dimensionedfor use in the patient treatment room to direct a particle beam providedthereto to a patient and having a curvature defining a particle beampath and a plurality of variable field magnets sequentially arrangedalong said beam tube for guiding the particle beam along said particlepath; a beam transport system for transporting the accelerated beam fromsaid accelerator to said patient treatment station; and a controller forcontrolling the magnetic field of said variable field magnets based onthe energy level of the particles in the accelerated beam.
 15. Aparticle beam therapy system as defined in claim 14, wherein each ofsaid variable field magnets of said gantry is a combined function magnetperforming a first function of bending the particle beam along saidparticle path and a second function of focusing or defocusing theparticle beam.
 16. A particle beam therapy system as defined in claim15, wherein said combined function variable field magnets of said gantryare arranged in triplets, each triplet comprising two focusing magnetsand a defocusing magnet disposed between said focusing magnets, saidfocusing magnets performing the combined function of bending theparticle beam and focusing the particle beam and said defocusing magnetperforming the combined function of bending the particle beam anddefocusing the particle beam.
 17. A particle beam therapy system asdefined in claim 16, wherein both said focusing magnets and saiddefocusing magnets are positive bending magnets for bending the particlebeam along an arc defined by a positive center of curvature, saidpositive center of curvature being oriented on the inside of the arc ofsaid beam pipe.
 18. A particle beam therapy system as defined in claim16, wherein said variable field magnets comprise: a superconducting coilwinding surrounding said beam tube, said superconducting coil windinghaving a geometry adapted to provide said combined function; and ahousing surrounding said superconducting coil winding, said housinghaving a curvature defined by a center of curvature and forming a beamtube receiving cavity having said beam tube supported therein.
 19. Aparticle beam therapy system as defined in claim 16, wherein said beamtube includes a particle beam entry point, a transition point, aparticle beam exit point, a first curved particle beam path arc lengthextending between said entry point and said transition point and asecond curved particle beam path arc length extending between saidtransition point and said exit point, said first arc length bendingabout ninety degrees and said second arc length bending about onehundred eighty degrees in a direction opposite said first arc length.20. A particle beam therapy system as defined in claim 19, furthercomprising: at least one scanning magnet disposed at a point about onehundred twenty degrees from said transition point along said secondcurved particle beam path arc length; and a superconducting variablefield magnet triplets disposed between said scanning magnet and saidbeam tube exit point, said superconducting variable field magnet tripletcomprising two focusing magnets and a defocusing magnet disposed betweensaid focusing magnets, said focusing magnets performing the combinedfunction of bending the particle beam and focusing the particle beam andsaid defocusing magnet performing the combined function of bending theparticle beam and defocusing the particle beam.